EMI/RFI Shielding and ESD Shielding with MicroGrid®
The Dexmet MicroGrid® EM series of expanded metal foils (EMFs) are versatile, effective materials for shielding against electromagnetic interference (EMI). EMFs are formed from solid metal foil in a proven, economical “slit-and-stretch” process. They are electrically continuous and, unlike knit or woven meshes, exhibit consistent and predictable conductivity. Thin, strong, flexible and lightweight, EMFs will not fray or unravel, and conform readily to complex surfaces, making them well-suited to composite manufacturing processes.
Standard configurations include copper, aluminum, nickel and Monel meshes at .002 and .003″ thick (50 and 75µm). Dexmet can readily produce custom types using other metals and foil thicknesses, including Cu and Al types down to .001″ (25µm). The open area of the mesh can be precision-tailored to meet user requirements for weight, resistivity, formability and shielding effectiveness.
Shielding Applications for MicroGrid®
- Shielding enclosures
- Ventilation screens
- Cable shielding
- Laminated structures
- Cockpit electronics
The key measure of merit for EMI shielding materials is “shielding effectiveness” (SE). SE is a measure of how well a material reduces (attenuates) Electromagnetic field strength.
The SE of expanded metal foils is dependent on several factors, including:
- Material type
- Foil Thickness
- Size of openings
- Openings per unit area
These parameters can be controlled during manufacturing to yield meshes custom-tailored for weight, resistivity and shielding effectiveness.
Download our Information Note to learn how shielding effectiveness is measured, and how MicroGrid® EM expanded foils can be tailored to your requirements.
Salt Solution Plating Tests
Mesh Per Inch (MPI)
Measure one inch and count the number of meshes (or openings – between two nodes) along the SWD direction. We generally refer to MPI in the SWD direction and not the LWD direction. See Standard Product Range for the mean MPI count for each Mesh Designation.
Openings Per Square Inch
Double the product of MPI and LWD mesh count. Openings per square inch = (3.5 x 2) x 2 = 14
Product Code Nomenclature
Product Example: 3 Ni 5-077
- Original Foil Thickness: 0.003 in.
- Metal or Alloy: Nickel
- Strand Width: 0.005 in.
- – LWD: 0.077 in.
Coverage Area Calculation
(Accurate to ±10%)
Coverage Area = 2 x MPI x Strand Width
Product Example: 2 x 24 x 0.005 = 0.24 Coverage Area = 24%
Open Area Calculation
(Accurate to ±10%)
Open Area = 1 – Coverage Area
Product Example: 1 – 0.24 = 0.76 Open Area = 76%
Weight Per Area Calculation
(Refer to Density of Materials Chart)
Grams per square inch = metal weight (Lbs per cubic foot) ÷ 12 x original foil thickness x 2 x MPI x strand width x 3.1416
Product Example: 554.688 ÷ 12 x 0.003 x 2 x 24 x 0.005 x 3.1416 = 0.10456 grams/sq. in.
Total Surface Area Calculation
A = Coverage Area
B = 85% of Original Foil Thickness
C = B/Strand width
D = Total Surface Area = 2A (1+C)
Product Example: A = 0.24
B = 0.85 x 0.003 = 0.00255
C = B/0.005 = 0.00255/0.005 = 0.51
Total Surface Area = 2 x 0.24 x (1+0.51) = 0.7248 sq. ft. of Surface Area per sq. ft. of MicroGrid®
Resistivity and Conductivity
See Resistivity and Conductivity Chart
Physical Testing of Expanded Metal Foil
The first rule in testing expanded metal and expanded plastic is the need for new rules. The standards of Ultimate Tensile, Yield Strength and Elongation do not necessarily apply. Simply establishing the area to be considered becomes a point of discussion. The solution is to eliminate the questionable areas and concentrate on what we know to be true. The tests are simple and do not generally require expensive equipment, so quality may be verified by our customers.
Tensile Testing to failure (Ultimate Tensile) is usually more of a shear test than a tensile test. Tensile Testing rips rather than pulls the strands apart. Depending on the configuration of the product, pulling the mesh may actually change it from one form to another. For example, a flattened metal foil will revert to its expanded configuration before failing.
Dexmet has established a simple yet effective test that utilizes the elasticity of the material. As the material is annealed, its elasticity, or spring-back, decreases. Relative stiffness can therefore be translated into degrees of anneal. A history has been developed that tells us whether we have accomplished a complete anneal. Feedback from our customers has also provided the specific numerical hardness requirements for a variety of processes. We know that certain rolling mill practices can adversely affect the ability of material to function in our process as well as in our customer’s applications. Testing has also shown that stress relieving will make the material feel softer and lay flatter but will not affect the bend recovery.
Pulling to within a small percentage of what would result in permanent deformation gives a reasonable measure of the force the material can tolerate without undue stretching. However, if stretching must be avoided entirely, pulling to the same distance a second time will result in the amount of force that the material can withstand without permanent deformation. This information can be very useful to the machine designer.
Salt Solution Plating Tests
The immersion of a sample of Nickel plated steel mesh in a bubbling 2% salt solution is an excellent test for plating quality. There is sufficient air to readily oxidize the nickel, but it is controlled. Salt Solution Testing remains one of the best methods for evaluating the post plating process. Exposure time provides a means to quantify the results.
Shielding Effectiveness Chart
Phone: (203) 294-4440
Fax: (203) 294-7899
22 Barnes Industrial Rd. So.
Wallingford, CT 06492
United States of America
SAMPE Seattle 2017
May 23-24, 2017
Washington State Convention Center,
Seattle, Washington – Booth# E42
Information on SAMPE Seattle 2017